Economically optimal nitrogen fertilization for yield and protein in hard red spring wheat

This analysis determines profit-maximizing N fertilization levels of hard red spring wheat (HRSW) (Triticum aestivum L.) for various wheat prices, N prices, and protein-based HRSW price premium/ discount (P/D) structures for southeastern Washington data. Fertilizer response data consisting of rates of N fertilization (kg ha(-1)), grain yield (kg ha(-1)), and grain protein (g kg(-1)) were used to statistically estimate regression relationships that predicted yield and protein in response to N. Experiments were located near Pullman, WA (550 mm average annual precipitation). All predicted net return maximizing N, protein, and yield levels were within the data range. Increasing P/D incentives for protein increased optimal N, the expected economic result. At the high P/D structures, the P/D structure dominated N and wheat prices in determining optimal N application levels. Overall, net return-maximizing yields varied only modestly with changes in both N and wheat price in this data set. However, in all scenarios, as P/D incentives increased, net return-maximizing N levels were beyond the level that resulted in maximum yield. At the two lowest P/D structures, which provided the lowest reward for protein, it was most profitable to fertilize for slightly less than 140 g kg-1 expected protein. These results indicate that it is not always profitable to use 14% protein as an N fertilization goal.